(1) Field of the Invention
The present invention relates to electrical circuits and particularly to circuits characterized by plural conductive paths supported on a non-conductive substrate. More specifically, this invention is directed to a method for the manufacture of electrical circuits from an intermediate comprising a layer of conductive material supported on a sheet of insulating material. Accordingly, the general objects of the present invention are to provide novel and improved articles and methods of such character.
(2) Description of the Prior Art
Techniques for the production of "printed" electrical circuits are well known in the art. One of the more common circuit fabrication techniques is photoresist etching wherein a laminate comprising a copper foil bonded to a non-conducting substrate is converted into a circuit board having the desired conductor pattern by a combined optical and chemical process. A photoresist process consists of the steps of coating the entire conductive surface of the laminate with either a negative or positive type resist material, positioning either a negative or positive type of film bearing in proper orientation relative to the resist layer, exposing the resist layer to light through the film, "developing" the resist layer in a multi-step procedure to expose the areas of the copper foil which are to be removed, chemically etching away the exposed copper and removal of the residual resist coating. Photo-resist techniques, such as that generally described, are limited as to production rate because of the large number of manufacturing steps, registration problems and because of the comparatively long time required to perform certain of the process steps. Furthermore, poor yield often results from careless performance of the step of removal of the residual resist coating.
It is further to be observed that prior art techniques, such as the photo-resist process generally described above, often require the performance of additional coating steps subsequent to removal of the residual resist material. Coating may be required to provide an insulating layer, in the form of a paint or varnish or a cover film, over the circuit conductors and the necessity of pattern matching may make the provision of such a coating a time-consuming operation which further disturbs productivity.
A further deficiency in the prior art resides in the fact that the conductive material exposed by removal of the residual resist coating is subject to oxidation and/or surface contamination by material such as oily dust. Such oxidation or surface contamination will impede the subsequent attachment of circuit elements to the formed circuit and thus must be guarded against by procedures which are both time consuming and labor intensive.